1. Field of the Invention
The invention relates to a wheel rim, more particularly to a bicycle wheel rim.
2. Description of the Related Art
An ideal bicycle wheel rim requires some features, including a relatively good rigidity, a relatively high strength, a relatively light weight, and a structure which facilitates insertion of a tire but which makes it difficult for the tire to be taken off. However, these features usually contradict one another.
As shown in FIG. 1, a conventional bicycle wheel rim 10 includes a pair of annular side walls 101, an annular base wall 102 interconnecting radial inner ends of the side walls 101, a pair of annular first extending walls 104 extending obliquely from the base wall 102 to a respective one of the side walls 101, and a pair of annular second extending walls 103 extending from a respective one of the first extending walls 104 to a corresponding one of the side walls 101. The middle portion of the base wall 102 protrudes radially and outwardly relative to the radial inner ends of the side walls 101. The presence of double extending walls results in a relatively high strength but a relatively heavy weight for the wheel rim 10. Moreover, the design of double extending walls also results in a relatively long radial depth (H) of an interior tire-retaining space such that, once an inserted tire 106 is punctured, a consequent deflation thereof can cause the tire 106 to be taken off easily. Furthermore, each of the extending walls 103 has a connecting segment 105 radially perpendicular to the base wall 102, thereby hindering sliding of tire beads 107 of the tire 106 during inflation.
As shown in FIG. 2, another conventional bicycle wheel rim 20 includes a pair of annular side walls 201, an annular base wall 202 interconnecting radial inner edges of the side walls 201 and forming an arch configuration, and an annular reinforcing wall 203 interconnecting radial outer parts of the side walls 201 and connected to the annular base wall 202. Each of the annular side walls 201 is thicker at a radial inner part that is connected to the base wall 202. The double-layer, i.e., the reinforcing wall 203 and the base wall 202, and the thicker parts of the annular side walls 201 result in a higher strength. Although the radial depth (H) of the interior tire-retaining space of this conventional wheel rim 20 is shorter than that of the previous conventional bicycle wheel rim 10, the disposition of the reinforcing wall 203 results in a relatively heavy weight for the conventional wheel rim 20.
FIG. 3 illustrates yet another conventional bicycle wheel rim 30 that includes a pair of annular side walls 301, an annular base wall 302 interconnecting radial inner edges of the side walls 301 and forming an arch configuration, and an annular reinforcing wall 303 interconnecting radial outer parts of the side walls 301 and connected to the annular base wall 302. The base wall 302 is thicker at left and right parts thereof that are connected respectively to the side walls 301. The double-layer, i.e., the reinforcing wall 303 and the base wall 302, and the thicker parts result in a higher strength. Although the radial depth (H) of the interior tire-retaining space of this conventional wheel rim 30 is shorter than that of the first conventional bicycle wheel rim 10, the presence of the reinforcing wall 303 results in a relatively heavy weight for this conventional wheel rim 30.
In co-pending U.S. patent application Ser. No. 11/726,841 filed by the applicant, there is disclosed a bicycle wheel rim including a pair of annular side walls, a pair of oblique walls that extend respectively from radial inner ends of the side walls, an annular base wall that interconnects the oblique walls, and a pair of annular connecting walls, each of which extends from the base wall and extends radially outward relative to a respective one of the oblique walls. The side walls cooperate with the oblique walls, the base wall, and the connecting walls to form a symmetrical truss structure with a relatively high strength. Additionally, since the interior space of the wheel rim of the co-pending application is relatively small, the deformation of a tire retained thereon that may cause the tire to be taken off the wheel rim will be effectively reduced. Moreover, when retaining the tire on the wheel rim of this application, since the connecting walls are oblique, tire beads of the tire can slide respectively and smoothly on the connecting walls during inflation of the tire.